Nowadays optical data transmission systems are transmitting optical signals with high data rates. However, high data rates require not only high bandwidths and expensive components at the transmitter and at the receiver but also degrade for a given modulation schema the signal quality according to the system and fiber impairments, e.g. filter distortions, chromatic and polarisation mode dispersion.
Different transmission methods like orthogonal frequency-diversity modulation OFDM or polarisation multiplex diversity are used to reduce the channel symbol rate and to overcome these impairments. But the realisation of these methods leads to complex systems.
Wavelength division systems split high data rate signals into two or more signals with lower data rates to overcome the impairments scaling with the data rate. But filters and different demodulators are necessary to separate and regain the data signals.
Caplan et al. OFC 2007, paper OThD3 describe a transmission method using only a single interferometer to demodulate several wavelength channels exploiting the periodic transfer function of an delay interferometer. Nevertheless separate filters and optical-electrical converters are still necessary for each channel.
The transmission methods may make use of different kinds of modulation, e.g. as intensity modulation, phase or difference phase modulation.
Especially difference phase shift keying DPSK is preferred for optical transmission systems. The performance of DPSK transmission is described by e.g. A. H. Gnauck and P. J. Winzer in IEEE Journal of Lightwave Technology, vol. 23, No. 1, pp. 115-130, January 2005.